This application claims the benefit of Japanese Patent applications No. 2002-091717 and No. 2002-219461 which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a lens barrel structured to extract a straight advancing motion from a rotary motion of a frame member and to perform an operation such as a lens extension, etc.
2. Related Background Art
In this type of lens barrel, a lens extension-and-reduction mechanism has hitherto been constructed of a multi-thread screw called a helicoid or a cam mechanism configured by cam pins and cam grooves.
FIG. 13 is a view showing the helicoid in development in one conventional lens barrel.
In this conventional lens barrel, a female helicoid member 10 having a female helicoid includes a first guide groove 10a for moving back and forth in the optical-axis directions corresponding to rotations, and a second guide groove 10b (a lead-0 portion) defined as a groove formed in a circumferential direction in continuation with the first guide groove 10a. 
FIG. 14 is a partially enlarged view of FIG. 9.
A male helicoid member 20 having a male helicoid engaging with the female helicoid of the female helicoid member 10, has a guide protruded portion 200 configured by surfaces 20a, 20b facing to the first guide groove 10a, and surfaces 20c, 20d facing to the second guide grooves 10b (the lead-0 portion).
The male helicoid member 20, when making the relative rotary motion to the female helicoid member 10 by the rotation of the female helicoid member 10, through engaging with the first guide groove 10a, moves in the optical-axis direction corresponding to the rotation. In an area of the second guide groove 10b (the lead-0 portion), the relative movement in the direction of rotation is made, however, no movement in the optical-axis direction is made. The function of the second guide grove 10b is, as disclosed in, for example, Japanese Patent Application Laid-Open No.11-23937, utilized for opening and closing a lens barrier.
FIGS. 15 through 17 are views showing a helicoid of another conventional lens barrel in development.
In this conventional lens barrel, a female helicoid member 10 having a female helicoid includes a helical groove 10a for moving back and forth in the optical-axis directions corresponding to rotations, and a circumferential groove 10b defined as a groove formed in the circumferential direction in continuation with the helical guide groove 10a. 
A male helicoid member 20, when making the relative rotary motion to the female helicoid member 10 by the rotation of the female helicoid member 10, through engaging with the first guide groove 10a, moves in the optical-axis direction corresponding to the rotation. In the circumferential groove lob, the relative movement in the direction of rotation is made, however, no movement in the optical-axis direction is made.
What is required of the conventional lens barrel described above is a contrivance for preventing the operation from becoming unstable due to interference with the helical groove 10a when the protruded portion of the male helicoid member 20 passes through the circumferential groove 10b. 
Further, it is also required that an incorrect helical engagement with an adjacent groove different from the predetermined position be avoided.
For meeting these requests, there has hitherto been adopted a configuration that the number of grooves is restricted, and the grooves are thinned out.
Moreover, the helicoid engagement is established by decreasing a length (an angle of rotation) of the circumferential groove 10b. 
Accordingly, the helicoid is unable to be disposed along the entire periphery, and an engaging area is reduced, resulting in a drop of engaging force. When receiving an external force, the helicoid might come off the engagement thereof.
Further, in an area where the helicoid engagement is attained, it is possible to shield the light that is to leak through a gap between the female helicoid member 10 and the male helicoid member 20. In an area where the helicoid engagement is not attained, however, a problem arises, wherein the light-shielding can not be performed, and a light shielding means is needed.
A further problem is that a non-groove area of the inner periphery of the female helicoid member 10 expands, and, when a beam of light is projected on this area, an intensive reflection occurs to cause a flare.
A still further problem is that the helicoid engaging areas can be provided merely in approximately three directions on the circumference because of the configuration of thinning out the helicoid grooves, and ununiform rotations are caused due to sinking in a recessed portion, etc. necessary for a secant relief of a die assembly, which is provided in the inner periphery of the female helicoid member 10.
A yet further problem is that the priority given to establishing the small number of engaging areas conduces to a restraint in terms of design.
It is a primary object of the present invention to provide a lens barrel capable of being formed with a multiplicity of grooves, attaining a stable helical engagement, obtaining a high engagement force, exhibiting an excellent light shielding characteristic and making difficult occurrences of the caused-by-stray-light flare, ghost, etc.
To accomplish the above object, according to one aspect of the present invention, a lens barrel includes a first cylindrical member having an inner peripheral surface, and a second cylindrical member internally fitted to the first cylindrical member and having an outer peripheral surface that facing in a radial direction to the inner peripheral surface of the first cylindrical member, wherein any one of the inner peripheral surface and the outer peripheral surface is formed with first and second grooves taking a helical shape and extending in an axial direction in parallel with each other, and a third groove extending in only a circumferential direction continuously from one side ends of the first and second grooves, the other of the inner peripheral surface and the outer peripheral surface are formed with first and second protruded portions engaging respectively with the first and second grooves in alignment in the circumferential direction and enabling relative rotations between the first and second cylindrical members and relative movements in the axial direction therebetween, the first and second protruded portions engage respectively with the first and second grooves with the result that the first and second cylindrical members make the relative rotations and the relative movements in the axial direction, and, when reaching the third groove, move through within the third groove, and the first and second cylindrical members are allowed to make only the relative rotations without moving in the axial direction, and the third groove includes a guide portion, formed in continuation from the first groove, for guiding the first protruded portion into the first groove.
In the lens barrel according to the present invention, preferably the second groove includes a portion, formed adjacent to the third groove, for inhibiting the first protruded portion from entering.
In the lens barrel according to the present invention, preferably a height of the first protruded portion is larger than a height of the second protruded portion, and the entrance inhibiting portion of the second groove has a depth set to permit the second protruded portion to pass through and to inhibit the first protruded portion from passing through.
In the lens barrel according to the present invention, preferably the guide portion is a groove bottom portion formed, in the third groove, having a depth set to permit the second protruded portion to pass through and to inhibit the first protruded portion from passing through.
In the lens barrel according to the present invention, preferably a length of the first protruded portion in an extending direction of the helical groove is larger than a length of the second protruded portion in the extending direction thereof, and a length of the third groove in the extending direction of the helical groove is larger than the length of the protruded portion on one side of the circumferential direction continuous with the first groove.
According to another aspect of the present invention, a lens barrel includes a first helicoid member including a high guide protruded portion provided on an inner surface or an outer surface of a cylinder and a low guide protruded portion lower in height than the high guide protruded portion, and a second helicoid member including a plurality of first guide grooves and a second guide groove that engage with the high guide protruded portion and/or the low guide protruded portion of the first helicoid member, the first guide grooves being formed in a helical shape on an engaging surface of the first helicoid member, the second guide groove being formed continuously with the first guide grooves in a circumferential direction, wherein the second guide groove partially includes a second middle guide groove, for abutting on the high guide protruded portion and guiding the same high guide protruded portion, formed in depth set to permit the low guide protruded portion to pass through and to make the high guide protruded portion unable to pass through so that the engagement between the first helicoid member and the second helicoid member is changed over from the engagement through the second guide groove to the engagement through the first guide grooves.
In the last mentioned lens barrel according to said another aspect of the present invention, preferably among the plurality of first guide grooves, the guide groove with which the low guide protruded portion engages includes a first middle guide groove formed in depth set to make the high guide protruded portion unable to pass through so as to inhibit the high guide protruded portion from entering and to enable the low guide protruded portion to pass through.
According to a further aspect of the present invention, a lens barrel includes a first cylindrical member, and a second cylindrical member fitted to the first cylindrical member, the first and second cylindrical members operating so as to consecutively change over a helical movement of moving along an axis of rotation while relatively rotating and a circumferential movement of making relative rotations with no movement in the direction along the axis of rotation, wherein the second cylindrical member includes a first crested portion and a second crested portion, and said first cylindrical member includes a first helical groove engaging with the first crested portion when making the helical movement, and a second helical groove provided adjacent to the first helical groove and engaging with the second crested portion, and the first and second crested portions make relative movements through the circumferential movement to positions to which the adjacent grooves are extended, and the second cylindrical member further includes guide portions for abutting on the first crested portion or the second crested portion and guiding the first and second crested portions so that the first crested portion and the second crested portion advance into the first helical groove and the second helical groove when changing over to the helical movement from the circumferential movement.
In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a first circumferential groove through which the first crested portion moves when making the circumferential movement, and a second circumferential groove through which the second crested portion moves when making the circumferential movement, the first crested portion is shorter in length in the direction along the axis of rotation than the second crested portion, and the first circumferential groove is narrower, enough not to permit the second crested portion to pass through, in width in the direction along the axis of rotation than the second circumferential groove.
In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a helical movement guide portion, formed in the vicinity of a boundary between the first circumferential groove and the second circumferential groove, for guiding the changeover from the circumferential movement to the helical movement in such a way that the second crested portion abuts thereon.
In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a circumferential movement guide portion, formed on the extension of the first helical groove and in the vicinity of the first circumferential groove, for guiding the changeover from the helical movement to the circumferential movement in such a way that the second crested portion abuts thereon.
In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a third crested portion formed in a range defined by the first helical groove, the second helical groove and the first circumferential groove, a fourth crested portion formed in a range defined by the first helical groove, the second helical groove and the second circumferential groove, and a fifth crested portion provided in a position facing to the third crested portion with the first circumferential groove interposed therebetween, the circumferential movement guide portion is formed by the fifth crested portion, and the helical movement guide portion is formed by the third crested portion and the fifth crested portion.